1. Field of the Invention
The present invention relates to an improved process for producing diamond powder by a shock compressing method.
2. Description of the Prior Art
The shock compressing method of producing a diamond powder is a process for producing a diamond powder by a shocking high pressure and high temperature which are instantaneously caused by a strong shock wave generated by a collision of a flyer plate propelled by a detonation of an explosive to a sample vessel.
A transformation of a carbon source into diamond by an impact compressing method has been considered to be a martenstic transformation for converting an atomic arrangement by slightly shifting adjacent atoms and contracting each layers distance of hexagonal network of graphite crystal in certain mutual relation and not to substantially cause a diffusion of carbon atoms. Therefore, in the conventional process for producing diamond powder by the shock compressing method, artificial graphite or natural graphite has been used as a starting material.
When the crystalline carbon source is used as the starting material, the following disadvantages have been found.
(1) A pressure of higher than 100 GPa is required to obtain an yield of diamond of more than 50%.
______________________________________ Shocking pressure Yield of diamond (GPa) (%) ______________________________________ 140 52-32 90 12 78 5 ______________________________________
(See G.B. Pat. No. 1,115,648)
(2) It is difficult to separate the resulting diamond powder from the unconverted graphite. For example, in the conventional process lead oxide as an oxidizing agent is admixed with the product obtained by the shock compression and the mixture is heated at about 450.degree. C. for 2 hours to oxidize the unconverted graphite and lead oxide is dissolved with acetic acid to separate diamond. Such complicated separating steps can be eliminated.